When you get to that weird green spider thing that tries to hide from you behind the pillars in Sanctuary of Rock and Lava, here is a tip:
Go to a pillar it's behind and have Rayman stand with his back facing the spider (doesn't matter if camera sees the spider or not). He will come and try to attack you. Blow as many shots into it as you can and then do it all again.
The spider 'thinks' you're not watching it; this way you don't need to spend 2 hrs chasing the thing between pillars.